He is accused of "orchestrating" the killing of the animals, in the Virunga National Park of the Democratic Republic of Congo, in 2007. Another two of them are missing.

Another institute member, who requested anonymity, said six foresters would also be questioned over the coming days on suspicion of having trapped and killed the animals in the site on Mashagiro's orders.

Local environment experts told AFP that "profound internal disagreements" within the conservation institute could lie behind the massacre.

"Some sector heads are involved in the trafficking of makala," said one.

Makala is a coal-like mineral illegally extracted from the forests these professional bodies are meant to protect.

The same source suggested that the gorillas could have been killed to create a diversion from this illicit trade -- or even to throw suspicion heat on rival park workers.

Alexandre Wathaut, the head of the institute, told AFP that the "fight against makala trafficking" from within the park had been "seriously stepped up" since late-2007.

He also acknowledged the existence of internal rivalries within the park's management.

The latest development is a departure from previous killings of the gorillas, when suspicion has fallen on local rebel forces.

Fierce fighting in the eastern Democratic Republic of Congo between government troops and forces loyal to a renegade ex-general has in the past been blamed for the slaughter of the rare animals.

A charity complained last year that fighting there between the leader of Tutsi forces, Laurent Nkunda and government troops meant rangers were having difficulty accessing the gorillas in the park.

The UNESCO-protected site is home to more than half of the last 700 mountain gorillas not in captivity.

Nkunda's men were accused by campaigners of eating two silverbacks in January 2007, but the motives for the other eight killings remain unclear.

Their bodies were found intact, sometimes with their young still alive and clinging to their bodies.